This invention relates to methods for midspan entry of optical fiber ribbons to access one or more optical fibers incorporated in the optical fiber ribbon.
Optical fiber ribbons include a plurality of individually coated optical waveguides, herein called optical fibers, which are held in parallel relationship to each other by an outer common coating. Each coated optical fiber typically includes a corn and cladding, primary and secondary coatings formed of plastic material, and an outer colored layer. The colored layer may be formed of a mixture of clear plastic material and pigment. Each coated optical fiber within a single optical fiber ribbon often is given a different color from that used in the other optical fibers in the ribbon in order that optical fibers within the ribbon may be identified and distinguished from each other. The outer common coating typically has two flat major surfaces separated by a thickness which is smaller than the width of the major surfaces.
Although some optical fiber ribbons have comprised a parallel array of coated optical fibers held between tapes, most optical fiber ribbons produced today comprise an outer common coating which encapsulates the coated optical fibers. The primary and secondary coatings, colored layer, and outer common coating may all be formed of ultraviolet curable materials. Urethane acrylate resins are frequently used as such ultraviolet curable materials. The coated optical fibers may be disposed in touching relation, or they may be completely separated by the outer common coating.
Optical fiber ribbons formed of optical fibers held between tapes can be relatively easy to peel in order to access the coated optical fibers therein. Accessing the coated optical fibers, particularly in the midspan of a cable, has been more difficult when they are encapsulated by the outer common coating. Therefore, efforts have been directed toward developing optical fiber ribbons in which the outer common coating may be removed from the coated optical fibers without damaging them. U.S. Pat. No. 4,176,910, assigned to Siemens AG, describes an optical fiber ribbon in which each coated optical fiber is coated by a layer of separating and lubricating material. Other publications also describe various methods for providing optical fiber ribbons which have good peelability of the outer common coating in order to reduce the difficulty in accessing the coated optical fibers.
Cables including optical fiber ribbons advantageously may benefit from mass splicing. However, traditional loose tube type optical fiber non-ribbon cables have not presented the problem of separating individual coated optical fibers from a ribbon. All advantages and disadvantages of each type of cable, and the possibility of future sheath entries in midspan, must be considered in order to select the optimal cable for a particular location. Labor costs for work in the field must be considered in the selection process.
A method for midspan entry of optical fiber ribbons is described in U.S. Pat. No. 5,460,683. This method includes placing a single or double sided adhesive tape on a support surface with its top surface having exposed adhesive. A plastic semi-flexible plastic card is secured to one end of the tape, and the tape and card are secured to a support surface. A length of optical fiber ribbon is placed on the exposed top surface of the tape and across the card. The portion of the ribbon overlying the card is lifted, and glue is placed on the card. The ribbon is then laid down onto the glue and the card. The ribbon is then lifted to cause the glue to rupture the common coating. By continuing to lift the ribbon, the lower common coating portion of the remainder of the ribbon length may be delaminated to access the coated optical fibers.
The adhesion of many prior art optical fiber ribbons which are not designed for easy peelability has so far been demonstrated to be too minimal to allow peeling by the method described in the '683 patent. While the method of the '683 patent causes an initial rupture of the common coating matrix, the peel does not sufficiently propagate beyond the card.
Another disadvantage of the method above described is that the card is not readily available and must be provided to the craftsperson in a midspan access kit. If the supply of cards becomes exhausted in the field, temporary expedients must be found. The craftsperson then must return to a supply area to obtain more cards, and possibly must wait until they can be shipped from a supplier.
Alternative methods include applying the glue directly onto a support surface and delaminating the optical fiber ribbon without the use of an adhesive tape. The support surface may be provided with upstanding sidewalls to aid in keeping the optical ribbon in line during lamination. However, the support surface then is littered with dried glue.